Melt blowing is a technique for forming fine diameter fibers from materials such as thermoplastic polymers, for example to prepare nonwoven material or to deposit adhesives. The technique conventionally involves extruding a thermoplastic material from a row of extrusion orifices extending along the lower edge of a melt blowing die. High velocity gas, typically air, is impinged on extruded polymer filaments exiting the extrusion orifices to attenuate the filaments and form small diameter filaments, or fibers. Conventional melt blown fibers are often 3-5 microns in diameter.
The melt blowing die, also referred to as a die assembly, conventionally includes a die tip (also referred to as a spinneret) that has extrusion orifices from which polymer melt is extruded and narrow extrusion channels that deliver polymer melt to the extrusion orifices. The die assembly also includes a die body, which is often in two halves, designed to distribute polymer uniformly to all extrusion orifices along the die tip. The die assembly also includes air plates on either side of the die tip to direct air to contact polymer extruding from the die tip and air manifolds for supplying air to the air plates. The die tip and die body halves are conventionally each made from large, single pieces of steel machined with necessary geometric features. The separate die tip and die body halves must then be assembled together to provide all of the necessary functionalities for an operable melt blowing die.
One problem with conventional melt blowing die assemblies is the difficulty of machining to prepare required fine geometries in large metal work pieces, which presents a significant practical limitation on the number and intricacy of geometries that can be included. Also, making such large machined pieces so that all necessary features precisely align and join when assembled into the final die assembly is difficult and expensive.
Some proposals have been made to use a plate assembly structure for one or more components of a die assembly, for example to make a die body in the form of a plate assembly that may mate with a separate die tip or a die tip in the form of a plate assembly that may mate with a separate die body. Utilizing a plate structure permits machining features in the smaller work pieces of the plates, reducing the need to machine large pieces. However, such proposed designs incorporating a plate structure still include separate pieces or subassemblies for corresponding die body, die tip and/or air functionalities that must be designed to match for a particular melt blowing die configuration and must be precisely aligned and joined together to operate for the particular design.